Technical Field
The present invention relates to a non-aqueous inkjet printing method in which printing is conducted by using a non-aqueous ink by an inkjet recording system.
Related Art
An inkjet recording system is a printing system in which printing is conducted by injecting a liquid ink having high fluidity from a fine nozzle to allow adhesion of the liquid ink onto a recording medium such as paper. This system has characteristics that this is a relatively inexpensive apparatus, and that a high-quality image having a high resolution can be printed at a high speed with low noises, and thus has been increasingly a part of modern life.
Color materials for inks used for inkjet recording systems are roughly classified into color materials using pigments and color materials using dyes. Among these, inks using pigments as color materials tend to increase since they are excellent in light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of solvents, inks are roughly classified into aqueous inks and non-aqueous inks. Non-aqueous inks that do not use water as an ink solvent, including solvent-based inks containing a volatile solvent as the main constituent and oil-based inks containing a non-volatile solvent as the main constituent, have gained attention since they have characteristics that they have fine stability on printing machines (intermittent discharge property, discharge restoration property after leaving a long period, and the like), they cause no curl on printing papers, they require a short time for the permeation and drying of the inks, and the like.
However, non-aqueous inks have a problem that the printing density is lowered since color materials easily permeate into printing media. Therefore, in order to improve the printing density, various suggestions have been made (for example, see JP 2010-1452 A). JP 2010-1452 A suggests a non-aqueous pigment ink containing non-aqueous resin dispersion microparticles having pigment dispersibility against an ink solvent. However, when a printing density is increased by the means of JP 2010-1452 A, other performances such as storage stability and ejection stability are deteriorated. Alternatively, it is also possible to increase a printing density by increasing a transfer amount of an ink, but a problem that the surface of a printed product is easily abraded (deterioration of abrasion resistance) occurs.
On the other hand, considerations for increasing a printing density by focusing on not an ink but a print method and devising the method have been made (see JP 2011-98454 A and JP 2012-161981 A). In either of the patent documents, a predetermined treatment liquid is imparted to a recording medium before or after formation of dots by an ink so that the treatment liquid overlaps with the ink during printing, whereby the permeation of the color material in the ink into the recording medium is prevented. JP 2011-98454 A suggests a pre-treatment liquid for a non-aqueous ink and JP 2012-161981 A suggests a post-treatment liquid for a non-aqueous ink, and either of these patent documents aims at improving a printing density.